1. Field of the Invention
The present invention relates to an external synchronizing system and a camera system using the external synchronizing system for operating the system based on a synchronizing signal on the basis of a television system provided from outside, particularly to an external synchronizing system and a camera system using the external synchronizing system which uses a compound synchronizing signal including a horizontal synchronizing signal and a vertical synchronizing signal as an external synchronizing signal.
2. Description of the Related Art
In a monitor camera system, normally, synchronization is established in a slave camera by using a synchronizing signal (horizontal synchronizing signal, vertical synchronizing signal, compound synchronizing signal including these) of a master camera. This is a well-known technology referred to as external synchronization. According to the external synchronization, there is carried out a processing of matching a phase of a synchronizing signal of the slave camera to that of a synchronizing signal of the master camera. In this case, finally, video signals are inputted from a plurality of cameras to one monitor.
However, there causes a difference in a time period for the synchronizing signal of the master camera to reach the respective slave camera owing to a difference in a delay amount of a transmission line in accordance with a location of installing the slave camera and when the slave camera is locked, there is produced an image causing a deviation in synchronization on the monitor.
Therefore, in each of the salve cameras, the deviation in the synchronization on the monitor is eliminated by carrying out phase adjustment relative to the synchronizing signal provided from the master camera such that an amount of the deviation in the synchronization caused on the monitor is absorbed. Further, based on the synchronizing signal which has been subjected to the phase adjustment, a synchronizing signal such as a horizontal synchronizing signal or a vertical synchronizing signal used on the side of the slave camera is formed.
Specifically, a horizontal synchronizing signal and a vertical synchronizing signal included in a compound synchronizing signal provided from the master camera are subjected to synchronizing separation, phase adjustment is carried out in respect of the horizontal synchronizing signal which has been subjected to the synchronizing separation, the phase of an internal horizontal synchronizing signal formed on the side of the slave camera is synchronized with the external horizontal synchronizing signal after the phase adjustment and in the meantime, a vertical counter for carrying out counting operation at a period of 1H (H; horizontal scanning time period) is reset by the vertical synchronizing signal which has been subjected to the synchronizing separation and a vertical synchronizing signal on the side of the slave camera is formed based on a count value since a load value (reset value) at resetting operation.
However, in a television system for carrying out interlace scanning, one screen (one frame) comprises two fields of an odd number (ODD) field and an even number (EVEN) field and as shown by FIG. 6, a format of the synchronizing signal differs depending on the odd number field and the even number field. When the format of the synchronizing signal differs depending on the field as mentioned above, when informing a vertical synchronizing signal on the side of the slave camera, the reset value which is loaded to the vertical counter in the resetting operation needs to differ depending on the odd number field and the even number field.
Therefore, whether the field in inputting the external compound synchronizing signal is the odd number field or the even number field, needs to determine and conventionally, the field is determined by a phase relationship between the vertical synchronizing signal and the horizontal synchronizing signal after the synchronizing separation. Specifically, there is used a field determining circuit having a constitution in which counting operation is carried out in synchronism with a horizontal synchronizing signal by using a counter and a field is determined by polarities of the horizontal synchronizing signal at a certain timing after detecting an edge of a vertical synchronizing signal.
However, according to the above-described conventional field determining circuit, there is constructed the constitution of using the counter, a number of gates are needed in fabricating the counter and therefore, there poses a problem in which the circuit scale is magnified and the cost is increased.
The present invention has been carried out in view of the above-described problem and it is an object thereof to provide an external synchronizing system and a camera system using the external synchronizing system capable of firmly determining a field by a simple circuit constitution.
According to an aspect of the present invention, there is provided a camera system for forming an internal horizontal synchronizing signal and an internal vertical synchronizing signal based on a compound synchronizing signal including a horizontal synchronizing signal and a vertical synchronizing signal provided from outside for carrying out an operation of the camera system in synchronism with the formed internal horizontal synchronizing signal and the formed internal vertical synchronizing signal, the camera system comprising a synchronizing separator circuit for separating the horizontal synchronizing signal and the vertical synchronizing signal from the compound synchronizing signal and outputting a first and a second pulse having a constant phase difference therebetween with one horizontal scanning time period as a unit with a horizontal synchronizing portion of the compound synchronizing signal as a reference, a first pulse forming circuit for forming a third pulse having a pulse width in correspondence with the phase difference between the first and the second pulses, a second pulse forming circuit for forming a fourth pulse at a timing of fall of the vertical synchronizing signal separated by the synchronizing separator circuit and a third pulse forming circuit for forming a field identifying pulse based on the third pulse and the fourth pulse.
According to the camera system having the above-described constitution, the first pulse forming circuit forms the third pulse which rises at a timing of the first pulse and falls at a timing of the second pulse. The third pulse constitutes a pulse for determining fields of odd number and even number. The second pulse forming circuit detects fall of the vertical synchronizing signal after synchronizing separation and forms the fourth pulse. The fourth pulse constitutes a pulse for detecting fall of the vertical synchronizing signal. Further, the third pulse forming circuit identifies the fields of odd number and even number in accordance with polarities of the field identifying pulse at a timing of the pulse for detecting fall of vertical synchronizing signal.
The present invention is applicable to a system constituted by any apparatus which needs to operate by establishing external synchronization by using a compound synchronizing signal other than a monitor camera system comprising a master camera and one or more of slave cameras. For example, there are conceived an external synchronization system in which the master apparatus is a camera and the slave apparatus are constituted by a plurality of VCRs and the external synchronization system in which both a master apparatus and one or more of slave apparatus are constituted by VCRs or Video Tape Recorders (VTRs) and so on.